I was shooting at a friends wedding and my shutter speed dial malfunctioned causing a 4 stop overexposure using TriX. The dresses were just white blobs. For fun I mixed up a proportional reducer and brought each roll to a normal development. I was impressed how well it worked. It is much harder to add density to negatives.
B&W print/negative film handles overexposure very well. That's the key point to understand, for someone new to this.
The best overall dynamic range I have found in the (high end) digital world is about 12 stops. When you compare that to old panatomic x film developed in POTA... well there is no comparison. That combination has been shown to provide up to 20 stops of range!!! If I remember correctly, POTA was developed for blast imaging.
But there is of course a lot more to this than dynamic range alone. What you will hear/read film photographers discussing is the toe and the knee of the tone curve (of film and also of photopaper). That tone curve provides a very different look, that many would say is more pleasing than the rather linear response you get from raw digital. In a nutshell, the tones ease into the highlights and the shadows quite gently- not abruptly and with posterization. Digital users must curve their linear scale to get that pleasing look; with film, it's built in. And every film has a different and characteristic 'look' with respect to knee and toe.
But the main point is how b&w print (neg) film handles overexposure. You can record lots of highlight detail.
P.S. I have an illustrative example from a few years ago that taught me a lot about this issue. I made a big mistake when shooting something on vacation. I had set up an infrared shot, using a deep infrared filter, and the (#87) filter cutoff was so deep that I needed a filter factor of many stops, 8 or 9 or so stops, as I recall. In other words, I timed the exposure to be 8-9 stops longer than sunny 16. And this was in high noon desert light, near Sedona, Arizona... virtually no clouds!
Problem was... in my haste to get the shot, I forgot to put on the bloody IR filter when I actually took the shot! So I overexposed by a ridiculous amount. I got my negs back from the lab and they were black to the eye. I mean it: black. Then I held one neg up to a lightbulb and could barely make out a wee bit of detail, so I thought, okay, why not scan it and see if there's anything there before I bleach the hell out of it and try to get something. So scan it I did. And voila... here's what a ~8-9 stop overexposed b&w film shot looks like... actually not half bad! Not pretty but.. hey it's an image.
Thank you all for your helpful comments.
Keith in your example of severe overexposure, you said your negatives was almost black. In normal circumstances to salvage this you need to do some special printing procedures isn't it? But if you just scan it on the computer I presume it would be almost black with almost zero detail right? My understanding is that the latitude advantage of black and white film is manipulated in the traditional developing and printing process but not in the scanner procedure.
I took a photograph of Half Dome in Yosemite National Park just after a snow storm. Before I took the photograph, I checked the light readings with a spot meter and found that the Subject Brightness Range [SBR] was 12 f/stops. I used Kodak Tri-X at box speed and developed normally in XTOL replenished. The film easily captured the full range without blowing out the highlights and catching details in the darkest parts. The tones of the clouds were different than the tones of the snow on the top of Half Dome. I have been told that film can handle 14 f/stops and I could see film covering 20 f/stops.
The latitude of b&w neg film is helpful in both workflows.
Originally Posted by mingaun
In the traditional workflow, you just "print through" the thick neg, i.e. you do a longer exposure to the paper. You will also need to do a contrast adjustment, e.g. print to multigrade paper and fiddle with contrast and perhaps do split grade printing. This is because all the info you want is bunched up in a narrow range of optical densities.
In the scan workflow, the optical density of the thickest (=most overexposed) negative is well within what most scanners can handle. A good flatbed can manage close to DMax 4 - about as dense as Velvia can get. Even a wildly overexposed b&w neg reaches nowhere near that optical density. So what happens is you scan the neg and find that the tones are all bunched up, but then you 'auto-level' the tones to try and get the right contrast. It is very easy. Actually easier than traditional route, I daresay... but not necessarily better ;) Anyway that is a topic for DPUG.
So... either way, the latitude of film real shines.
There are, of course, consequences of overexposure. But the point is that you can overexpose a neg film quite severely and still get a usable image. And even if you don't overexpose wholesale, another point is that little specular highlights will be held in detail, e.g. highlights on jewelry or a wedding dress, chrome on a car, reflections on water, etc...
When shots are overexposed like Keith's (I've done the same thing with IR820 and leaving the filter off, I seem to do it once every couple of rolls), you just need to use a longer exposure in the enlarger. The very dense negative lets the light through slowly, so it just takes longer for an image to form on the paper. Same principle in scanning - a film scanner has an exposure control which controls how long the scanner's CCD is exposed to the negative. Dense negatives just need more exposure.
As you can see, it's become very grainy and of poor contrast, particularly in the highlights, but you can tell what is there. If you did that much overexposure (even 4 stops = 16x, not even the 8 stops = 256x here) with digital or slide film, you would have a perfect white field from which absolutely nothing was recoverable.
Thank you all for your helpful information. Things are getting much clearer now to me. Also now i realise how important a spot meter is for black and white. I can at lest ensure the darkest scene with detail will be exposed correctly. Too bad there is no small spot meter in the market.
Originally Posted by mingaun
With respect, you are over-thinking this. You won't see most of the benefit from a spot meter until you are a lot more experienced with film and your camera. As a beginner, I would strongly suggest that you concentrate first on getting the correct exposure for mid-tones and highlights, because they will have the biggest influence on how your photographs look. Incident meters or averaging reflected light meters are fine for that purpose.
Last summer I had my Canonet set for indoor conditions at f/1.7 and 1/60th of a second. I accidentally left it on that setting and took a picture of a fish I caught outdoors during the day. By my calculations that's at least 8 stops of overexposure. I figured it was a lost cause but when I attempted to print it, I did get a picture that was recognizably a fish... I wouldn't recommend it unless you know what you are asking for; the picture was pretty grainy with cooked highlights but honestly a lay person would probably think it was fine.
Here is a little bit more info on B&W negative film latitude, demonstrating the film's insensitivity to overexposure as well as its sensitivity to underexposure.